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authorSean Christopherson <seanjc@google.com>2022-02-02 00:49:41 +0000
committerPaolo Bonzini <pbonzini@redhat.com>2022-04-13 13:37:47 -0400
commit1aa0e8b144b6474c4914439d232d15bfe883636b (patch)
tree86b81233c708ebaf91b32300b290dcfaa867c289 /init
parentc24a950ec7d60c4da91dc3f273295c7f438b531e (diff)
Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug
Add a config option to guard (future) usage of asm_volatile_goto() that includes "tied outputs", i.e. "+" constraints that specify both an input and output parameter. clang-13 has a bug[1] that causes compilation of such inline asm to fail, and KVM wants to use a "+m" constraint to implement a uaccess form of CMPXCHG[2]. E.g. the test code fails with <stdin>:1:29: error: invalid operand in inline asm: '.long (${1:l}) - .' int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; } ^ <stdin>:1:29: error: unknown token in expression <inline asm>:1:9: note: instantiated into assembly here .long () - . ^ 2 errors generated. on clang-13, but passes on gcc (with appropriate asm goto support). The bug is fixed in clang-14, but won't be backported to clang-13 as the changes are too invasive/risky. gcc also had a similar bug[3], fixed in gcc-11, where gcc failed to account for its behavior of assigning two numbers to tied outputs (one for input, one for output) when evaluating symbolic references. [1] https://github.com/ClangBuiltLinux/linux/issues/1512 [2] https://lore.kernel.org/all/YfMruK8%2F1izZ2VHS@google.com [3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98096 Suggested-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20220202004945.2540433-2-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'init')
-rw-r--r--init/Kconfig5
1 files changed, 5 insertions, 0 deletions
diff --git a/init/Kconfig b/init/Kconfig
index ddcbefe535e9..b19e2eeaae80 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -77,6 +77,11 @@ config CC_HAS_ASM_GOTO_OUTPUT
depends on CC_HAS_ASM_GOTO
def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
+config CC_HAS_ASM_GOTO_TIED_OUTPUT
+ depends on CC_HAS_ASM_GOTO_OUTPUT
+ # Detect buggy gcc and clang, fixed in gcc-11 clang-14.
+ def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
+
config TOOLS_SUPPORT_RELR
def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)